The present invention relates to a holding mechanism of an optical element, an optical apparatus, such as an exposure apparatus, which uses the holding mechanism, and a device manufacturing method. The present invention is suitable, for example, for a holding mechanism that holds the optical element, such as a lens and a mirror, used for a semiconductor exposure apparatus.
The semiconductor exposure apparatus is an apparatus that transfers an original (such as a reticle), which has a circuit pattern, onto a substrate (such as a silicon wafer). A projection lens is used to transfer or image the reticle pattern onto the wafer, and should have a high resolving power so as to manufacture highly integrated circuits. Thus, a lens in the semiconductor exposure apparatus needs to have reduced aberration, uniformities of various characteristics relating to the glass material and film, and working and assembly precisions of the glass surface shape.
A barrel that holds the lens and/or mirror is generally made of metal or another material different from glass. FIG. 9 is a partially sectional and perspective view of a barrel structure for an optical system in a conventional semiconductor exposure apparatus. In FIG. 9, plural lenses 101 and 102 are fixed onto and supported by metal frames 103 and 104. These metal frames 103 and 104 are stacked in a cylindrical holding member 105 through air gap adjusting spacers 106, and pressed and fixed from the top by pressure screw rings 107 and 108. Japanese Utility Model Application, Publication No. 3-96609, for example, discloses a method for fixing an optical element without adhesive. Japanese Patent Application, Publication No. 2002-48962, for example, discloses a lens structure that has a circumferential notch and attempts to remove a distortion of the lens effective diameter.
Some optical apparatuses, such as a projection optical system in a semiconductor exposure apparatus, need a high optical characteristic. In order to minimize a deformation of an optical element and the deterioration of its optical characteristic due to the external force, each optical element, such as a lens, in the optical system, is usually fixed by adhesive that has little shrinkage on curing, onto a metal frame without applying the external force to the optical element. Nevertheless, exposure that uses a laser with a short wavelength might cause gas emissions from the adhesive, contaminating the optical element surface, and deteriorating the transmittance and the optical characteristics. In exchanging each optical element during manufacturing/maintenance of the exposure apparatus, steps of peeling off adhesive and reapplying the adhesive deteriorate the yield.
Japanese Utility Model Application, Publication No. 3-96609, discloses a method of fixing an optical element without adhesive. However, the groove formed in the glass and a spherical member that contacts the groove cannot fix the lens in the optical-axis direction and may shift the lens due to the acceleration perpendicular to the optical axis. One solution for this problem is to apply a large power to the top surface of the lens, but this power would consequently deform the lens and generate greater birefringence in the lens.